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Development of a structurally well-defined small molecule with a high oxygen reduction reaction catalytic activity is a key approach for the bottom-up design of a metal-free carbon-based catalysts for metal-air batteries and fuel cells. In this paper, we characterize the oxygen reduction reaction activities of trioxotriangulene derivatives, which are stable neutral radicals with high redox abilities, via rotating disk electrode measurements in alkaline aqueous solution. Among trioxotriangulene derivatives having various substituent groups, N-piperidinyl-substituted derivative mixed with acetylene black shows a high catalytic activity with the two-electron transferring process exceeding other derivatives and quinones. To reveal the correlation between molecular structure and catalytic activity, we discuss substituent effects on the redox ability of trioxotriangulene derivatives, and demonstrate that a molecule with electron-donating groups yields relatively higher catalytic activities. Catalytic oxygen reduction is an important process for clean energy production. Here the catalytic activity of trioxotriangulenes for the oxygen reduction reaction is shown to be correlated with their redox potential, offering a potential route to rationally tune their catalytic activity.

We have investigated the motion of growing pentacene single crystals in solution under various electric fields. The pentacene single crystals in 1,2,4-trichlorobenzene responded to the electric field as if they were positively charged. By optimizing the strength and frequency of an alternating electric field, the pentacene crystals automatically bridged the electrodes on SiO2. The pentacene crystal with a large aspect ratio tended to direct the [1̅10] orientation parallel to the conduction direction, which will be suitable from a viewpoint of anisotropy in mobility. The present result shows a possibility of controlling the position and orientation of organic single crystals by the use of an electric field, which leads to high throughput and low cost industrial manufacturing of the single crystal array from solution.

We proposed a novel but facile method for growing organic semiconductor single-crystals via solvent vapor annealing (SVA) under electric field. In the conventional SVA growth process, nuclei of crystals appeared anywhere on the substrate and their crystallographic axes were randomly distributed. We applied electric field during the SVA growth of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) on the SiO2/Si substrate on which a pair of electrodes had been deposited beforehand. Real-time observation of the SVA process revealed that rodlike single crystals grew with their long axes parallel to the electric field and bridged the prepatterned electrodes. As a result, C8-BTBT crystals automatically formed a field effect transistor (FET) structure and the mobility reached 1.9 cm(2)/(V s). Electric-field-assisted SVA proved a promising method for constructing high-mobility single-crystal FETs at the desired position by a low-cost solution process.

We have investigated the film morphology and the field effect mobility of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) thin films which were formed by spin coating on the SiO2 substrate with solution-processed graphene electrodes. The domain size and the density of aggregates in the C8-BTBT film showed the same dependence on the spinning speed. These competitive two factors (domain size and density of aggregates) give an optimum spinning speed, at which the field effect mobility of C8-BTBT transistor showed a maximum (2.6 cm2/V s). This result indicates the importance of spinning speed in the fabrication of solution processed organic thin film transistors by spin coating.